Plant derived cyclic terpenoids including monoterpenoids derived from geranyl diphosphate, sesquiterpenoids derived from farnesyl diphosphate and diterpenoids derived from geranylgeranyl diphosphate, comprise a significant class of secondary metabolites that mediate a plant's interaction with its environment. From a health related perspective, these compounds also represent an important class of potential antibiotic, antifungal and anti tumor agents. The objective of our research is to understand as completely as possible the structural, functional and chemical features governing two distinct stereochemically controlled cyclizations of farnewyl diphosphate (FPP) catalyzed by two highly homologous plant sesquiterpene cyclases that result in two unique bicyclic products.